Are there any physical limitations that would prevent the existence of photosynthetic multicellular animals? Something like a euglena, except multicellular?
Maybe having a high enough surface area/volume ratio (like a leaf) in a large animal is a major obstacle?
ideas?
A coral reef has a multitude of animals that use photosynthesis in their tissues. Taken as a whole they are quite large. Cite
Here is a jellyfish that incorporates algae in it’s body.
Jellyfish Lake, Palau
Animals move. Muscular action consumes a large portion of metabolism: the cellular fuel in a fuit or vegetable takes days or weeks to store, and an animal burns it up in hours.
I doubt if a macroscopic animal with even 100% of it’s skin seeded symbiotically with chloroplasts could photosynthesize enough energy to keep the animal breathing, much else walking around.
Don’t we photosynthesize vitamin D from cholesterol?
But some extra energy would be better than none, and so it would be an evolutionary advantage. Would it cost us more energy/resources to maintain the chloroplasts than they could provide in the way of energy?
Founder effect?
Once the motile life forms began using consumption of other life forms for sustenance, the particular accident that happened to develop photosynthesis did not tend to repeat on that side of the evolutionary line?
We have a few coaral (the jellyfish are symbiotes) where something linke that did occur and we have venus flytraps on the other side of the line, but most lifeforms simply used the sustenance system of their parents.
Flytraps photosynthesize for cellular fuel. The insectivorous habit gains them nitrogen, which they need because their habitat is nitrogen-poor.
Probably. At the cellular machinary level, simply having a feature means that some portion of the cell’s total activity is devoted to developing and maintaining that feature. And in the end it’s a question of specializing in one or the other of opposite survival strategies: sit there and slowly soak up sunlight, or go out and find some fuel. Jellyfish and corals can have symbiotic algae because they have high surface area ratios and don’t expend a lot of energy. But for almost anything else it just isn’t worth it.
That doesn’t fall within the definition of “photosynthesis.” Photosynthesis is the fixation of carbon from simple molecules using sunlight, not the transformation of more complex organic molecules into others.
It might be pointed out that no multicellular organisms, or even unicellular organisms other than bacteria, are actually photosynthetic in and of themselves. It is generally believed that even the chloroplasts of algae and multicellular plants represent an ancient symbiosis with photosynthetic bacteria.
Since photosynthesis was first invented by bacteria, other organisms have generally taken the route of becoming photosynthetic by symbiosis with organisms that already had it rather than developing it from scratch. This includes algae and higher plants with their choroplasts, as well as the fungi that adopted a symbiosis with algae to form lichens, as well as a wide range of animals including corals, clams, and others that also formed symbioses with algae.
As has been mentioned, this strategy is probably only effective for sedentary or slow-moving organisms. Actively-moving organisms require a higher rate of energy production than photosynthesis can supply.
There are photosynthetic hydra, and I have read about microscopic worms that have symbiotic plants in their skin, and lack a mouth because they can get all the nutrients they need through the skin. I can’t recall the name or find a link, unfortunately. Like photosythesis itself, that trick takes a lot of relative surface area to pull of.
At least for larger animals, another problem is how they tend to have something covering the skin; fur, scales, an exoskeleton, etc. That doesn’t stop something like a sloth from having plant life on it’s fur, but plant life on the fur isn’t going to help sustain an animal directly. I’m sure there are ways that one could get around this ( a symbiote taking the place of fur with something like grass, say, or transparent scales or exoskeletons ), but it’s an extra evolutionary hurdle.
And another problem on land is that plant life isn’t that likely to end up inside the body, save by being eaten; it doesn’t often end up in a place where it can set up shop and evolve into symbiosis.
Maybe not.
Wouldn’t it have the potential for us to over-consume energy even more than we already do, leading to even greater obesity than we are struggling with already?
For most of our history, include the period we’d evolve such a thing, no. For almost all of history the problem has been avoiding starvation, not obesity.
That’s probably why we have a problem with obesity; we’re not really evolved to handle overabundance.